Metallic container with an integral split-electrode series-laminated heater

ABSTRACT

The electrical heater is provided for heating containers of food. The wall of the container may constitute a portion of the heater structure or the heater may be composed of three laminated structures fastened to a food container. The heater has a split electrode, both parts on the same side of an electrically conductive material. On the opposite side of the conductive material is the wall of the container or a conductive sheet. Principal current flow is from one of the split electrodes through the conductive layer to the large conductive sheet and then back through the conductive layer to the second split electrode.

United States Patent [72] Inventor Nathaniel E. Hager, Jr.

Lancaster, Pa.

[21 1 Appl. No. 861,694

(22) Filed Sept. 29, 1969 [45] Patented Aug. 10, 1971 [73] AssigneeArmstrong Cork Company Lancaster, Pa.

[54] METALLIC CONTAINER WIT I-I AN INTEGRAL SPLIT-ELECTRODESERIES-LAMINATED UNITED STATES PATENTS 1,978,089 10/1934 Jones PrimaryExaminerVolodymyr Y. Mayewsky Attorney-Clifford B. Price ABSTRACT: Theelectrical heater is provided for heating containers of food. The wallof the container may constitute a portion of the heater structure or theheater may be composed of three laminated structures fastened to a foodcontainer. The heater has a split electrode, both parts on the same sideof an electrically conductive material. On the opposite side of theconductive material is the wall of the container or a conductive sheet.Principal current flow is from one of the split electrodes through theconductive layer to the large conductive sheet and then back through theconductive layer to the second split electrode.

PATENTED AUG] 01971 INVENTOR NATHANIEL E. HAGER, JR.

ATTORNEY METALLIC CONTAINER WITH AN INTEGRAL SPLIT- ELECTRODESERIES-LAMINATED HEATER BACKGROUND OF THE INVENTION to a laminatedheater which is to be used with a food container.

2. Description of the Prior Art Laminated-type electrical heaters havebeen disclosed in the prior art, for example, in U.S. Pat. No.3,264,595, wherein there is disclosed a three-electrode laminatedheater. Also, there has been utilization of heating devices inconjunction with packages for foodstuffs as shown in U.S. Pat. No.3,296,415. Such structures have even utilized laminated-type heaterswith both electrodes on the same side of the laminated structure.

It is the object herein to provide a heater which may be in combinationwith a food container for the purpose of providing an efficient andcommercially successful heater which may be fastened to the underside ofa food container to rapidly warm the material within the container. Theheater must readily adapt to an electrical generator or power source forthe purpose of supplying the current necessary for the heater to operateto deliver heat at a uniform rate per unit area. The heater must becapable of receiving the normal rough handling that is associated withhigh-speed production lines, and finally, the heater must provide forrapid heating of the foodstuff within the container with minimum poweroutput.

SUMMARY OF THE INVENTION The invention is directed to the heaterstructure which may be used with a food container and may actuallyincorporate a wall of the container. The heater is formed by the use oftwo separated electrodes, preferably of the same area, which areconductively bonded on the same side of a conductive layer. On theopposite side of the conductive layer is conductively bonded aconductive sheet or coating which covers the complete opposite side ofthe conductive layer. Current flow is from one of the split electrodesthrough the conductive layer tothe conductive coating, along theconductive coating, back through the conductive layer to the secondsplit electrode. The flow of the current causes heat to be generated byelectrical resistance, and this heat will be transmitted to thefoodstuff within a container to which the heater may be fastened. Thewall or bottom of the container may actually be used as the conductivecoating on the conductive layer. IN the open market, the food containerwill be sold with the heater an integral part thereof and, due to itslow cost, the heater will be disposable along with the food container.The split-electrode structure will permit the heater to readily connectwith the contacts of an electrical generator for the purpose ofproviding power to the heater. By having both electrodes in aside-by-side relationship, the need for leads from the electrodes to thepower supply is eliminated and, in actual practice, the container withthe foodstuff and heater need only be placed on a receptacle which ispart of the power supply to provide the connecting coaction between thepower supply and the heater. Positioning of the heater on the bottom ofa food container helps cause rapid heating due to heat flow byconvection in the liquid-containing food.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a view of the heater whereinFIG. 1A is a top view, FIG. 1B is a cross-sectional view, and FIG. IC isa bottom view of the heater, and

FIG. 2 is a view of a modification of the heater incorporated with afood container.

DESCRIPTION OF THE PREFERRED EMBODIMENT The heater structure is shown inFIG. 1. The split electrodes are semicircular in shape as shown in FIG.1C, and these split electrodes 2 and 4 are spaced from each other by adistance which exceeds the thickness of the conducting layer 6 so thatthere is no overheating in the gap area due to excessive current flowfrom split electrode 2 through layer 6 to split electrode 4 without thecurrent passing through layer 8. However, the gap should not be toogreat or else there will be a lack of heating in the center portion ofthe heater where the gap exists. The gap width is adjusted so heating inthe gap region caused by current flow parallel with the electrodesequals heating elsewhere due to current flow perpendicular to theelectrodes. An approximate calculation indicates the gap width should beequal to twice the conductive layer thickness if the material isisotropic, and greater if the material conductivity parallel to theelectrodes exceeds that perpendicular to the electrodes. The twoelectrodes 2 and 4 are fastened to one surface of the conductivematerial 6 and lie within a flat plane. On the opposite surface of theconductive material or layer 6, there is fastened a conductive coatingor sheet 8 which covers the complete upper surface of layer 6, as bestseen in FIG. IA.

FIG. 2 is a modification of FIG. 1 wherein the conductive coating 8 hasbeen replaced by a wall of the container 10 holding food 11. This wall12 of food container 10 is placed in direct contact with the conductivelayer 6. In both the embodiments of FIG. 1 and FIG. 2, a conventionalelectrical generator 14 is connected to the split electrodes 2 and 4.

Obviously, other configurations other than the semicircular structurefor the split electrodes could be used as long as two separateelectrodes exist and they are properly spaced from each other, result inuniform heating across the conductive sheet 8, permit a current flowfrom one split-electrode configuration through the conductive layer andto the conductive coating 8 and then back through the conductive layer 6to the other split electrode and also permit enough current to flow inthe gap region parallel with the electrodes to heat that region.

By changing the relative area relationship of the two parts of the splitelectrode, the rate of heat per unit area may be varied or proportionedin the areas above the split electrodes. Total heat output for a givenarea may be varied by modifying the resistivity or thickness of theconductive layer.

The metallic foil electrodes of the present invention may be made fromany suitable electrically conductive metal foil having a thicknessgenerally in the range of 0.000l-0.0l inch. Metal foils of aluminum,copper, stainless steel, tin-plated steel, and the like may be used. Theconductive coating may also be made of the same materials as were theelectrodes.

The conductive layer may be fabricated of any material having therequisite resistivity and capable of maintaining a good bond andelectrical contact with the opposing sheet electrodes. A suitablematerial is that described in U.S. Pat. No. 3,264,595. Another suitablematerial is a product called Temsheet, a trademark product of ArmstrongCork Company. The Temsheet is made by a beater saturation process usingcellulosic fibers, although asbestos fibers may be used. Anyconventional process such as the so-called alum-ammonia process, may beused to beater saturate the fibers with a suitable amount of theelastomeric binder. A conductive material, usually acetylene black, isintroduced into the fibrous slurry prior to the deposition of the rubberbinder onto the fibers. Conventional papermaking procedures are usedthroughout. The final sheet after suitable drying, and perhaps pressing,conducts electricity and generates heat due to the sheets resistance.The resulting sheet can serve as a heating element. The sheet isanisotropic having an electrical volume resistivity of 7.8 ohms-in. forcurrent flow parallel with the face of the sheet and 67 ohms-in. forcurrent flow perpendicular to the face of the sheet.

In one specific heater which has been used in conjunction with a foodcontainer, the heater was made as a 2%-inch disc with a 0.125-inch gapbetween the split electrodes. The conducting layer was 0.033-inchTemsheet having an electrical volume resistivity of 67 ohm-in. asmeasured in the direction perpendicular to the electrodes. Theelectrodes were 0.0008- inch copper foil bonded with a simplecarbon-loaded electrical-conducting adhesive. The same adhesive was usedto bond the aluminum wall of the food container to the top surface ofthe conductive layer. The heater had a resistance of 2 ohms as measuredbetween the two split electrodes. When a voltage of volts was connectedto the two halves of the bottom split electrodes, a current of 5 ampsflowed and total power used was 50 watts. Obviously, the heater need notonly be used in conjunction with food containers, but has use as ageneral purpose heater.

Whatl claim is:

l. A combined disposable container and electrical heater structurecomprising a single use disposable metallic container having asubstantially flat continuous bottom end portion, a flat continuouselectrically conductive layer of compacted,

water-laid fibrous material with electrically conductive resistancematerial incorporated therein conductively attached to the outer surfaceof said bottom end portion of said container, and substantiallyconforming in shape and linear dimensions thereto, and two flatspaced-apart electrodes conductively mounted on the outer surface ofsaid fibrous electrically conductive layer and adapted to be connectedto a source of electrical current whereby electrical current is passingbetween the electrodes through the electrically conductive layer and themetallic bottom end portion of the container, said electrodes being ofequal surface area and of sufficient size and shape to coversubstantially the entire surface of said fibrous conductive layer withthe exclusion of the area located between the electrodes, the areabetween the electrodes being of a width such that excess current willnot flow therethrough and yet will allow heat to be generated in thearea at substantially the same rate per unit area as heat is generatedin the region above the electrodes.

1. A combined disposable container and electrical heater structurecomprising a single use disposable metallic container having asubstantially flat continuous bottom end portion, a flat continuouselectrically conductive layer of compacted, water-laid fibrous materialwith electrically conductive resistance material incorporated thereinconductively attached to the outer surface of said bottom end portion ofsaid container, and substantially conforming in shape and lineardimensions thereto, and two flat spaced-apart electrodes conductivelymounted on the outer surface of said fibrous electrically conductivelayer and adapted to be connected to a source of electrical currentwhereby electrical current is passing between the electrodes through theelectrically conductive layer and the metallic bottom end portion of thecontainer, said electrodes being of equal surface area and of sufficientsize and shape to cover substantially the entire surface of said fibrousconductive layer with the exclusion of the area located between theelectrodes, the area between the electrodes being of a width such thatexcess current will not flow therethrough and yet will allow heat to begenerated in the area at substantially the same rate per unit area asheat is generated in the region above the electrodes.